1. Field of the Invention
The present invention relates to a method for producing a 3-methylthiopropanal by reacting an acrolein with a methyl mercaptan. 3-Methylthiopropanal is useful as an intermediate for producing a methionine as a feed supplement, a hydroxy analogue thereof (e.g., 2-hydroxy-4-methylthiobutanoic acid) and the like.
2. Description of the Background Art
Conventionally, a method of reacting an acrolein and a methyl mercaptan using an acid/base mixed catalyst is known as one of methods for producing a 3-methylthiopropanal. For example, U.S. Pat. No. 2,776,996 describes a method of supplying an acrolein and an acid into a mixture which has been prepared by mixing a methyl mercaptan and a base at a molar ratio of acid/base of 0.05 to 10. GB Patent No. 1,166,961 describes a method of supplying a methyl mercaptan into a mixture of an acrolein, an acid and a base, and a method of co-supplying an acrolein, a methyl mercaptan, an acid and a base. In both methods of the GB Patent, the base is used in excess amount than that of the acid. Further, U.S. Pat. No. 6,031,138 describes a method of co-supplying an acrolein, a methyl mercaptan, an acid and a base while using the base in equimolar amount to that of the acid.
However, these method have problems such that by-products having high boiling points tend to be produced and the resulting 3-methylthiopropanals do not necessarily get satisfactory quality.